Digital circuits made of III-IV semiconductor FETs and the like have been demonstrated to have superior speed and power performance and are used in applications such as super computers. However, the power consumption of this type of device needs to be improved. Complementary HFETs are known for low power consumption and are expected to provide high speed capabilities. It is therefore beneficial to be able to fabricate Complementary HFETs in an efficient and relatively inexpensive manner.
In their article entitled "Complementary Heterostructure Insulated Gate FET Circuits for High-Speed, Low Power VLSI", IEDM 86, page 448 Daniels et al disclose a well known complementary HIGFET structure. Although this structure is capable of relatively high-speed operation and consumes reduced amounts of power, there are basic problems associated with the fabrication and operation thereof. Although source and drain fabrication is self-aligned to gates, ohmic contact formation is not self-aligned at all. The ohmic contacts further comprise different metals for the P contacts and the N contacts. Finally, no local interconnect is provided so that regions of one device may be coupled with regions of another.
U.S. Pat. No. 4,830,980 entitled "Making Complementary Integrated P-MODFET and N-MODFET" issued to Hsieh on May 16, 1989, discloses a relatively high speed structure. The method for fabricating complementary MODFETS includes implanting a portion of an N channel with P type ions of sufficient dosage to transform the portion into a P channel. Again, different ohmic metals are used for the P contacts and N contacts and the formation of the ohmic contacts is not self-aligned to the gates. Furthers, no local interconnects are provided.
In view of the above, it is highly desirable to have complementary HFETs wherein the fabrication of the sources, drains and ohmic contacts is self-aligned to the gates and local interconnects are provided as part of a multi-level interconnect-system for sub-micron VLSICs and ULSICs. This technology allows for further improvements in density, speed and power consumption.